The goal of this project is to identify the role of selectins in the trafficking and responses of Th1, Th17, and CD8 cells to nonpathogenic and pathogenic doses of influenza viruses in the lungs. These viruses are highly contagious, and cause yearly epidemics worldwide, with sporadic, devastating pandemics. This past influenza season in the northern hemisphere saw the emergence of a new triple reassortant H1N1 influenza strain carrying swine, avian, and human segments. This virus is now causing a worldwide pandemic. Amid growing concern that the new H1N1 virus will become more virulent and the possibility human of human transmission highly pathogenic H5N1 avian virus could occur, it is crucial to develop new strategies to control the morbidity and mortality associated with influenza viruses. Although CD4 and CD8 T cells typically control influenza virus infection in the lungs via cytotoxic- and cytokine-mediated responses, highly pathogenic strains can cause potent and aberrant inflammatory responses to which T cells contribute. It is therefore critical to understand how T cell responses to pathogenic vs nonpathogenic influenza viruses differ in the lungs to identify mechanisms that could be targeted to ameliorate pathological responses of T cells to this infection. Surprisingly little is known about the regulation of T cell trafficking into the lungs in the response to influenza viruses or how the magnitude of inflammation could affect their function. Our studies of the murine model of influenza have shown that Th1 and Th17 cells arise in the primary response with doses of virus that produce immunity and limited morbidity as well as with doses that are highly pathogenic. In the model of immunity, these effector cells, as well as responding CD8 cells, acquire the capacity to bind P-selectin, an endothelial selectin which initiates migration into sites of inflammation. In the absence of functional selectin ligands or PSGL-1 (P-selectin glycoprotein ligand-1), a major ligand for selectins on T cells, CD4 T cells have aberrant expansion and elevated production of IFN-3 and IL-17 in the draining LN, as well as greatly impaired accumulation in the lungs. The data suggest the hypothesis that selectin-ligand interactions could have a dual role in regulating T cell trafficking into the lungs as well as in dampening the effector response. In this application, we propose in vivo and in vitro studies to test this hypothesis using mice that are deficient in PSGL-1, or are unable generate functional selectin ligands, IFN-3 and IL-17 reporter mice, selectin fusion proteins, and WT and engineered influenza viruses. These tools will enable us to assess the responses CD4 cells and CD8 cells in the following specific aims: 1) to evaluate the role of selectins in T cell trafficking and localization in the lungs after infection with non-pathogenic and pathogenic doses of influenza virus;and 2) to determine the role of selectins regulating the responses of effector T cells. We hope to gain new insights into the regulation of effector T cells through mechanisms that control adhesion via selectins that could be targeted to help protect the population from the consequences of pathogenic influenza viruses. PUBLIC HEALTH RELEVANCE: If we find previously unidentified roles for selectins T cell recruitment or responses in the lungs after influenza infection, we will have identified a new mechanism of T cell regulation in the pulmonary response to this virus. If targeting of cells via selectins can reduce inflammation, synthetic selectin inhibitors that are already in use in murine models of disease might offer a new clinical approach to control pathogenic responses to influenza viruses.